[exim] Batv and sender verify fail

Hi,

I have implemented BATV (Exim 4.67) and it has been working correctly.
Many mail servers though still bounce to From: address. Anyway, I am
having a problem with one mail server that has rejected an email with a
complaint that sender could not be verified. Here's the bounce message:

 lynn.luker@???
    SMTP error from remote mail server after MAIL
FROM:<prvs=TLaPoint/094487f619@???> SIZE=115784:
    host mail.llalaw.com [199.72.78.4]: 578
prvs=TLaPoint/094487f619@??? address rejected with
reverse-check

Here are my null sender rcpt and local_parts statements which occur
before any other denies:

        deny    local_parts   = ^.*[@%!|] : ^\\.

        # Nullsender - signed return-path not signed
        warn    log_message = address must be signed for this sender.
                senders = :
                local_parts = +batv_list

        # Nullsender - signed return-path prvscheck invalid
        deny message = Invalid reverse path signature.
                senders = :
                control = caseful_local_part
                condition  = ${prvscheck
{$local_part@$domain}{BATVKEY}{1}}
                !condition = $prvscheck_result

        # Nullsender - accept signed
        accept  senders = :
                control = caseful_local_part
                condition  = ${prvscheck
{$local_part@$domain}{BATVKEY}{1}}
                condition = $prvscheck_result
                set acl_m7BA = 0
                set acl_m3 = 0

        # Nullsenders check recipients
        accept  senders = :
                domains = +local_domains
                set acl_m3 = 0
                endpass
                local_parts = ${lookup mysql{MYSQL_CHECK}}

As you can see the only deny is if the signed address is in error, or if
there is no such recipient. I don't see why sender verify would fail. I
believe the Exim list verifies sender, and I have no problem sending to
the list.

Any ideas?

Thanks.
Craig